Vibration At Cold Idle ?

[jigmaster flash]

bit of a weird one here, hope someone can shed some light!

last couple of weeks I have noticed a rhythmic (2 secs on/2 secs off) low vibration that i can hear and feel inside the car through the drivers seat and floor - it occurs ONLY ON A COLD STARTUP (that must be a clue!) and disappears completely after about 5 mins (once engine gets a little heat in it)

rpm and engine note are stable and fine at both cold and warm idle.

any ideas what i should check lads?

cheers

marty

[Ruud]

My first guess would be gearbox mount

[jigmaster flash]

cheers ruud, i will have a gander at the tranny mount next time its on the lift.

i dismissed the tranny (+engine) mount as there are no other symptoms, and i'd have expected a knackered tranny mount to show symptoms on acceleration or with gear/throttle linkage ?

marty

[Ruud]

_{Don't pin me down on it though - vibration is always a grey area as it travels. I take it the vibration does not occur when you put it in drive?}

[steve2006]

My project 1994 was doing a similar thing which disappeared after replaced the 2 precat O2 sensors which had open circuit heaters but did not illuminate the engine management light.

I put it down to the ECU not knowing the correct fueling lamda and causing the symptom.

A quick code read should confirm if any related codes are stored.

[jigmaster flash]

yes ruud, the vibration is not felt if put into any drive gear - does that re-inforce the tranny mount suggestion ?

Steve if the o2 sensors were malfunctioning i presume the symptoms would be present regardless of gearbox selection?

[The-Acre]

yes ruud, the vibration is not felt if put into any drive gear - does that re-inforce the tranny mount suggestion ?

Steve if the o2 sensors were malfunctioning i presume the symptoms would be present regardless of gearbox selection?

Just a thought, as the exhausts, especially around the flange are known to blow, could that have a slight effect? The reason I mention it, is that when I had a slight (and I mean very slight) uneven idle, the mechanic noticed the very slight exhaust blow, and said it could have an effect on the idle. As he was trained by Lexus, I guess he should know?

[Mybikes a cx500]

My project 1994 was doing a similar thing which disappeared after replaced the 2 precat O2 sensors which had open circuit heaters but did not illuminate the engine management light.

I put it down to the ECU not knowing the correct fueling lamda and causing the symptom.

A quick code read should confirm if any related codes are stored.

Sounds like it matched the symptoms

[jigmaster flash]

Cheers Phil but the idle speed is rock solid stable so don't think exhaust leak is the culprit. While i'm under the car next week i'll check anyway.

i'm half swaying to the mount suggestion, half to a closed/open loop problem which could be caused by a multitude of things. (fingers crossed for the tranny mount as its a cheap and easy fix!)

[Torkasmax]

Greetings,  hate to drag an old thread up, but My 2000 LS400 have this exact issue.  The car is new to me and is a choice example, all maint records (dealer maintained, garage kept).  Very odd problem, cyclic or ON-off-ON, like a waveform.  Vibration, doesn't feel like a miss.  Only on cold start up, gone when up to operating temp.  Dead smooth in fact.

I would like to hear from the OP what was the fix??

Thanks

Andrew